Gap-filling with uniform properties

ABSTRACT

During semiconductor fabrication homogeneous gap-filling is achieved by depositing a thin dielectric layer into the gap, post deposition curing, and then repeating deposition and post deposition curing until gap-filling is completed. Embodiments include depositing a layer of low deposition temperature gap-fill dielectric into a high aspect ratio opening, such as a shallow trench or a gap between closely spaced apart gate electrode structures, as at a thickness of about 10 Å to about 500 Å, curing after deposition, as by UV radiation or by heating at a temperature of about 400° C. to about 1000° C., depositing another layer of low deposition temperature gap-filled dielectric, and curing after deposition. Embodiments include separately depositing and separately curing multiple layers.

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing semiconductordevices exhibiting high reliability and uniform gap-filling. The presentinvention enjoys particular applicability in fabricating high density,multi-level, flash memory devices with improved gap-filling.

BACKGROUND OF THE INVENTION

Semiconductor memory devices, such as erasable, programmable, read-onlymemories (EPROMs), electrically erasable programmable read-only memories(EEPROMs), and flash erasable programmable read-only memories (FEPROMs)are erasable and reusable, and are employed in various commercialelectronic devices, such as computers, cellular telephones and digitalcameras. There has recently evolved devices termed mirrorbit deviceswhich do not contain a floating gate electrode. In mirrorbit devices,the gate electrode is spaced apart from the substrate by anoxide/nitride/oxide (ONO) stack, such as a silicon oxide/siliconnitride/silicon oxide stack. In such devices the charge is containedwithin the nitride layer of the ONO stack. The relentless drive forminiaturization has led to the fabrication of various types of flashmemory devices comprising transistors having a gate width of about 150nm and under, and gate structures spaced apart by a gap of 225 nm orless. Conventional practices comprise forming a sidewall spacer on sidesurfaces of the gate stack, thereby reducing the gate gap to about 25nm.

As device dimensions shrink into the deep sub-micron regime,vulnerability to mobile ion contamination, such as hydrogen iondegradation, increases, and it becomes increasingly more difficult tosatisfactorily fill high aspect ratio gaps between neighboringtransistors, as well as to satisfactorily fill high aspect ratioopenings, such as shallow trenches for trench isolation structures andgaps between metal lines, such as bit lines and aluminum lines. Theinability to adequately getter mobile ion contaminants, such as hydrogenions, results in a neutralization of electrons and, hence, leakagecausing programming loss as well as a charge gain causing reappearanceof erased information. The inability to adequately fill gaps betweenneighboring transistors leads to void formation and an open contact withconsequential shorting between contacts causing leakage and lowproduction yields.

A pre-metal dielectric layer or first interlayer dielectric (ILD₀) istypically deposited over gate electrode structures filling the gaps,followed by rapid thermal annealing. Conventional practices comprisedepositing a boron-phosphorous-silicon oxide derived from tetraethylorthosilicate (BPTEOS) or a phosphorous doped high density plasma(P-HDP) oxide as the ILD₀. However, such oxides fall short of addressingboth the mobile ion contamination and void formation problems.

The inability to satisfactorily fill other various openings and gapsduring semiconductor fabrication leads to various problems, includingvoid formation and short circuiting. There have recently becomeavailable various low deposition temperature dielectric materialsdesigned to fill high aspect ratio openings and gaps, such as openingsand gaps having an aspect ratio of 3:1 or greater. Such materialsinclude, for example, Aziva Flowfill materials manufactured by AzivaTechnology, Inc. located in Newport, England; and HARP (AppliedMaterials High Aspect Ratio Fill Process) available from AppliedMaterials located in Santa Clara, Calif. Other conventional spin-onmaterials designed to fill high aspect ratio openings include BPTEOS,boron-doped silicon oxide derived from tetraethyl orthosilicate (BTEOS);and phosphorous-doped silicon oxide derived from tetraethylorthosilicate (PTEOS). Such materials are conventionally deposited andthen subject to post deposition annealing in order to increase thedensity of the deposited material, improve wet etch characteristics andimprove moisture resistance. However, the effective deposition of suchmaterials in high aspect ratio openings remains problematic, because thedeposited material within the opening, typically at the bottom of theopening, does not exhibit the same properties as the deposited materialat the top of the opening or at a distance from the opening. As a resultof such a difference in properties or inhomogeneities, the dielectricmaterial proximate the bottom of the filled opening exhibits a wet etchrate significantly greater than the wet etch rate of the dielectricmaterial in other areas, such as at the upper portion of the filledopening or at a distance from the opening. Further, it was found thatafter curing voids existed in the bottom of the opening. Suchnonuniformities and voids lead to various problems, including shortcircuiting and leakage, as well as low production yields.

Accordingly, there exists a need for methodology enabling thefabrication of semiconductor devices with improved reliability,increased operating speed, reduced device leakage and homogenouslydeposited dielectric layers filling gaps and openings. There exists aparticular need for methodology enabling the fabrication of flash memorydevices, such as mirrorbit devices, with improved data retention,increased operating speed, reduced device leakage, homogeneously filledgaps and openings, and improved reliability.

DISCLOSURE OF THE INVENTION

An advantage of the present invention is a method of fabricating asemiconductor with uniform gap-filling and improved reliability.

Additional advantages and other features of the present invention willbe set forth in the description which follows and in part will beapparent to those having ordinary skill in the art upon examination ofthe following or may be learned from the practice of the presentinvention. The advantages of the present invention may be realized andobtained as particularly pointed out in the appended claims.

According to the present invention, the foregoing and other advantagesare achieved in part by a method of manufacturing a semiconductordevice, the method comprising: depositing a first layer of dielectricmaterial into an opening of a layer or into a gap between elements;curing the deposited first layer of dielectric material; depositing asecond layer of dielectric material on the deposited first layer ofdielectric material and into the gap; and curing the deposited secondlayer of dielectric material.

Embodiments of the present invention include depositing at least oneadditional layer of dielectric material into the opening or gap, e.g., atotal of three to six layers, and separately curing each additionallayer of dielectric material after it is deposited. Embodiments includedepositing each dielectric material at a thickness of about 10 Å toabout 500 Å, e.g., at a thickness of about 250 Å to about 500 Å, andthen curing each layer after it is deposited, as by heating at atemperature of about 400° C. to about 1000° C., or by UV radiation.Embodiments further include depositing plural layers with intermediatedeposition curing in forming a shallow trench isolation structure,filling gaps between closely spaced apart gate electrode structures,including mirrorbit devices, as well as filling gaps between conductivelines, such as aluminum lines and poly bit lines.

Additional advantages of the present invention will become readilyapparent to those skilled in this art from the following detaileddescription wherein embodiments of the present invention are describedsimply by way of illustration of the best mode contemplated to carry outthe present invention. As will be realized, the present invention iscapable of other and different embodiments, and its several details arecapable of modifications in various obvious respects, all withoutdeparting from the present invention. Accordingly, the drawings anddescription are to be regarded as illustrative in nature, and not asrestrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a gap-filling problem attendant uponconventional practices.

FIG. 2 schematically illustrates a problem attendant upon conventionalSTI implementation.

FIGS. 3 and 4 schematically illustrate a gap-filling embodiment of thepresent invention.

FIGS. 5 and 6 schematically illustrate another gap-filling embodiment ofthe present invention.

FIGS. 7 through 9 schematically illustrate an STI embodiment of thepresent invention.

FIGS. 10 through 12 schematically illustrate another STI embodiment ofthe present invention.

In FIGS. 3 through 6, similar features are denoted by similar referencecharacters.

In FIGS. 7 through 12, similar features are denoted by similar referencecharacters.

DESCRIPTION OF THE INVENTION

The present invention addresses and solves various reliability problemsattendant upon conventional semiconductor fabrication techniques. Theseproblems arise as device dimensions continue to shrink, creating closelyspaced apart elements, such as gate electrode stacks or conductivelines, with high aspect ratio gaps or high aspect ratio openings inlayers, e.g., STI.

Conventional semiconductor fabrication techniques comprise depositingvarious dielectric materials at a relatively low deposition temperature,e.g., at a temperature of about 0° C. to about 600° C., to fill highaspect ratio openings or gaps, such as Aziva Flowfill, HARP, as well asBPTEOS, BTEOS and PTEOS. However, upon annealing the deposited gap-fillmaterials, voiding and non uniformities occur, notably an increase inthe wet etch rate at the bottom of a filled opening or gap.

For example, adverting to FIG. 1, there are illustrated two gateelectrode structures on substrate 10. Each gate electrode structurecomprises a gate dielectric layer 11, a floating gate 12, and interpolydielectric, such as a silicon oxide/silicon nitride/silicon oxide (ONO)stack, and a control gate electrode 14. Reference character 15 denotes ametal silicide, such as cobalt silicide. Each gate electrode stacktypically comprises sidewall spacers, such as a silicon oxide liner 16and layer of silicon nitride 17. The gap between the gate electrodestructures is filled by depositing a premetal dielectric or firstinterlayer dielectric (ILD₀) 18, followed by post deposition curing, asat a temperature of about 400° C. to 1000° C. Such post depositionannealing is implemented in order to increase the density of thedeposited dielectric layer, improve the wet etch rate and to improve theability of the deposited layer to resist moisture absorption. However,it was found that in the area proximate the bottom of the gap,designated by reference character “X”, voiding occurs. Further, it wasfound that in the area designated by “X”, the wet etch rate issignificantly greater than the wet etch rate at the top of the openingor at a location remote for the opening, as at the location “Y”.

A similar problem exists when implementing STI techniques, as shown inFIG. 2. A shallow trench 21 is formed in substrate 20 and filled with adielectric material 22. After post-deposition annealing, the bottom ofthe opening, designated by reference character “X”, typically exhibitsvoiding and/or an increased wet etch rate vis-à-vis the material at theupper portion of the filled opening. Such voiding and nonuniformitiesoccur throughout semiconductor fabrication when filling a gap or anopening, such as a gap between poly bit lines or aluminum lines.

The present invention addresses and solves such nonuniform gap-fillingproblems by strategically depositing the gap-fill material in aplurality of layers and conducting a separate post deposition cure aftereach layer is deposited. It was found by depositing plural dielectriclayers with intervening post deposition curing, each thin layer iscompletely cured and, hence, exhibits uniform properties, such as auniformly low wet etch rate, and voiding is prevented.

Embodiments of the present invention comprise depositing a plurality ofthin dielectric layers, as at a thickness of about 10 Å to about 500 Å,e.g., about 250 Å to about 500 Å, with separate post deposition curingof each deposited layer to fill openings and gaps having a high aspectratio, e.g., an aspect ratio 3:1 or greater. Embodiments of the presentinvention comprise depositing, for example, two to six separatedielectric layers, with post deposition curing after each dielectriclayer is deposited, e.g., three to five dielectric layers.

Curing can be conducted in any conventional manner, as by heating at atemperature of about 400° C. to about 1000° C. Such annealing can beimplemented in a furnace or oven, in an atmosphere of nitrogen, steam(H₂O), or a forming gas containing nitrogen and hydrogen, or by rapidthermal annealing. Post deposition curing can also be implemented byexposure to UV radiation.

In accordance with embodiments of the present invention, each entirethin layer is fully cured so that the deposited dielectric materialexhibits a uniformly low wet etch rate throughout the entire filmthickness. Embodiments of the present invention enable the fabricationof semiconductor devices having uniform properties while avoiding thegeneration of voids during gap-filling.

The expression “gap-fill” or “gap-filling” is intended to encompassvarious aspects of semiconductor fabrication in which a dielectricmaterial is deposited into an opening or a gap. In accordance withembodiments of the present any of various conventional dielectricgap-fill materials can be employed. When filling gaps between closelyspaced apart gate electrode structures, such as in flash memorymirrorbit devices with gate electrodes comprising a gate dielectricstack (ONO) with a gate electrode thereon, it is desirable to deposit afirst dielectric layer with a relatively high boron content for improvedfluidity, particularly in situations where undercut portions exist inthe sidewall spacers, and to deposit a subsequent dielectric layerexhibiting a high phosphorous content for improved gettering of mobileion contaminants, such as hydrogen ions. Accordingly, in embodiments ofthe present invention involving memory devices, such as mirrorbitdevices, the first and second dielectric layers can comprise BPTEOS,wherein the first dielectric layer contains a higher concentration ofboron than the second dielectric layer but a lower phosphorous contentthan the second dielectric layer. Embodiments of the present inventioninvolving memory devices also include depositing a first dielectriclayer of BTEOS, post deposition curing, and depositing a seconddielectric layer of PTEOS, followed by post deposition curing.

Mirrorbit technology is fundamentally different and more advanced thanconventional floating gate technology, thereby enabling innovative andcost-effective advancements. A mirrorbit cell doubles the intrinsicdensity of a flash memory array by storing two physically distinct bitson opposite sides of a memory cell, typically within the nitride layerof the ONO stack of the gate dielectric layer separating the gate fromthe substrate. Each bit within a cell serves as a binary unit of data,e.g., either 1 or 0, mapped directly to the memory array. Reading orprogramming one side of a memory cell occurs independently of whateverdata is stored on the opposite side of the cell. Consequently, mirrorbittechnology delivers exceptional read and write performance for wirelessand embedded markets.

An embodiment of the present invention applied to a flash memorymirrorbit device is schematically illustrated in FIGS. 3 and 4, whereinsimilar features are denoted by similar reference characters. Advertingto FIG. 3, spaced apart gate electrode stacks of a mirrorbit device areformed on substrate 110. For illustrative convenience, the associatedsource/drain regions are not illustrated. Each gate electrode stackcomprises a gate dielectric layer 111 formed of a composite ONO stackcomprising silicon oxide layer 111A, silicon nitride layer 111B, andsilicon oxide layer 111C, and a gate electrode 114 formed thereon.Typically, sidewall spacers are formed on side surfaces of the gateelectrode stack, which sidewall spacers can include a silicon oxideliner 116 and silicon nitride spacers 117. A metal silicide layer 115,such as cobalt silicide or nickel silicide, can be formed on the gateelectrode 114.

With continued reference to FIG. 3, in accordance with embodiments ofthe present invention, a first layer of dielectric material 120 isdeposited, as at a thickness of about 10 Å to about 500 Å, e.g., about250 Å to about 500 Å. First dielectric material 120 can be any ofvarious dielectric materials designed for filling high aspect ratioopenings. In accordance with embodiments of the present invention, firstdielectric layer 120 can be BTEOS or BPTEOS with a relatively high boronconcentration for improved gap-filling. After depositing the firstdielectric layer 120, post deposition curing is conducted, as byannealing at a temperature of about 400° C. to about 1000° C. Becausefirst dielectric layer 120 is very thin, uniform properties are achievedupon post deposition annealing, such that dielectric layer 120 exhibitsa uniformly low wet etch rate and uniform density across its entirethickness. Further, by depositing plural dielectric layers withintermediate post deposition curing of each deposited layer, voiding atthe bottom of the gap between the gate electrode structures is avoided.

Adverting to FIG. 4, a second dielectric layer 130 is deposited, such asPTEOS or BPTEOS. Upon employing BPTEOS for layer 120 and layer 130,layer 120 which contain a higher boron content than layer 130 and alower phosphorous content than layer 130. Layer 130 would desirablycontain a higher phosphorous content for improved gettering of mobileion contaminants, such as hydrogen ions. Subsequent to depositing layer130, post deposition curing is conducted. Post deposition curing ofdielectric layer 130 can be implemented in a manner similar to postdeposition curing of layer 120. Subsequently, chemical mechanicalpolishing (CMP) is conducted resulting in the structure illustrated inFIG. 4.

Another embodiment of the present invention applied to a mirrorbitdevice is schematically illustrated in FIGS. 5 and 6. Features in FIGS.5 and 6 similar to those appearing in FIGS. 3 and 4 bear similarreference characters and are not described again. In accordance withthis embodiment of the present invention, a first layer of dielectricmaterial 140 is deposited followed by post deposition curing.Subsequently, a second layer of dielectric material 150 is depositedfollowed by post deposition curing. Subsequently, as illustrated in FIG.6, a third layer of dielectric material 160 is deposited, followed bypost deposition curing. Subsequently, CMP is implemented resulting inthe structure illustrated in FIG. 6. It should be understood thatalthough three different layers of dielectric material are deposited inthe embodiment illustrated in FIGS. 5 and 6, a greater number ofindividual dielectric layers can be deposited with post depositionannealing conducted after depositing each dielectric layer, such as fromthree to six layers, or even more.

Another embodiment of the present invention related to STI isschematically illustrated in FIGS. 7 through 9, wherein similar featuresbear similar reference characters. Adverting to FIG. 7, a shallow trench210 is formed in semiconductor substrate 200. Subsequently, a thermaloxide liner 220 is formed in the trench in a conventional manner. Inaccordance with an embodiment of the present invention, a first layer ofdielectric material 230 is deposited followed by post deposition curing.As in the previously illustrated embodiments, each layer of dielectricmaterial can be deposited at a thickness of about 10 Å to about 500 Å,e.g., about 250 Å to about 500 Å. Post deposition curing of depositedlayer 230 can be implemented, as by heating at a temperature of about400° C. to about 1000° C.

Subsequently, as illustrated in FIG. 8, a second dielectric layer 240 isdeposited followed by post deposition curing. Deposited layer 240 can becured in the same manner as layer 230. Subsequently, CMP is implementedresulting in this structure illustrated in FIG. 9.

Another embodiment of the present invention related to STI isillustrated in FIGS. 10 through 12 wherein similar features bear similarreferences characters. Adverting to FIG. 10, a shallow trench 210 isformed in semiconductor substrate 200 and a thermal oxide liner 220formed therein. Subsequently, a first dielectric layer 250 is depositedfollowed by post deposition curing to obtain uniform properties andensure a uniformly high etch rate throughout the thickness of layer 250.Subsequently, second dielectric layer 260 is deposited followed by postdeposition curing for homogenization.

A third dielectric layer 270, as shown in FIG. 11, is then depositedfollowed by post deposition curing for homogeneity. Subsequently, asillustrated in FIG. 12, CMP is implemented to form the completed STIstructure.

The present invention is applicable in various of stages ofsemiconductor fabrication wherein a dielectric layer is deposited withinan opening or a gap. Embodiments of the present invention ensure thatgap-filling is implemented without generating voids and to ensure thatuniform properties are obtained throughout the entire thickness of thedielectric layer, particularly a uniform high etch rate.

The present invention provides methodology enabling the fabrication ofsemiconductor devices, particularly flash memory devices, such asmirrorbit devices, exhibiting improved reliability with homogeneousgap-filling. Semiconductor memory devices produced in accordance withthe present invention enjoy industrial applicability in variouscommercial electronic devices, such as computers, mobile phones,cellular handsets, smartphones, set-top boxes, DVD players andrecorders, automotive navigation, printers and peripherals, networkingand telecom equipment, gaming systems, and digital cameras.

In the preceding detailed description, the present invention isdescribed with reference to specifically exemplary embodiments thereof.It will, however, be evident that various modifications and changes maybe made thereto without departing from the broader spirit and scope ofthe present invention, as set forth in the claims. The specification anddrawings are, accordingly, to be regarded as illustrative and notrestrictive. It is understood that the present invention is capable ofusing various other combinations and environments and is capable ofchanges or modifications within the scope of the inventive concept asexpressed herein.

1. A method of fabricating a semiconductor device, the methodcomprising: depositing a first layer of dielectric material into a gapbetween two spaced apart gate electrode structures; curing the firstdeposited layer of dielectric material; depositing a second layer ofdielectric material on the first deposited layer of dielectric materialand into the gap; curing the deposited second layer of dielectricmaterial, wherein: the first dielectric layer comprises boron andphosphorous-doped tetraethyl orthosilicate (BPTEOS); the seconddielectric layer comprises BPTEOS; the first dielectric layer contains agreater amount of boron than the second dielectric layer; and the seconddielectric layer contains a greater amount of phosphorous than the firstdielectric layer.
 2. The method according to claim 1, wherein each layerof dielectric material is deposited at a thickness of about 10 Å toabout 500 Å, and each layer of dielectric material is cured after it isdeposited by either heating at a temperature of about 400° C. to about1000° C. or exposing the layer to ultraviolet (UV) radiation.
 3. Themethod according to claim 1, wherein each gate electrode structurecomprises a dielectric sidewall spacer on side surfaces thereof.
 4. Themethod according to claim 1, wherein the first and second dielectriclayers comprise the same dielectric material.
 5. The method according toclaim 1, wherein the first and second dielectric layers comprisedifferent dielectric materials.
 6. The method according to claim 3,wherein each gate electrode structure further comprises: a gatedielectric stack comprising a first oxide layer, a nitride layer on thefirst oxide layer, and a second oxide layer on the nitride layer; and agate electrode on the gate dielectric stack.
 7. The method according toclaim 5, wherein each dielectric layer comprises the same dielectricmaterial.
 8. A semiconductor device prepared by a process comprising:depositing a first layer of dielectric material into a gap between twospaced apart gate electrode structures; curing the first deposited layerof dielectric material; depositing a second layer of dielectric materialon the first deposited layer of dielectric material and into the gap;curing the deposited second layer of dielectric material, wherein: thefirst dielectric layer comprises boron and phosphorous-doped tetraethylorthosilicate (BPTEOS); the second dielectric layer comprises BPTEOS;the first dielectric layer contains a greater amount of boron than thesecond dielectric layer; and the second dielectric layer contains agreater amount of phosphorous than the first dielectric layer.
 9. Thesemiconductor device of claim 8, wherein each layer of dielectricmaterial is deposited at a thickness of about 10 Å to about 500 Å, andeach layer of dielectric material is cured after it is deposited byeither heating at a temperature of about 400° C. to about 1000° C. orexposing the layer to ultraviolet (UV) radiation.
 10. The semiconductordevice of claim 8, wherein each gate electrode structure comprises adielectric sidewall spacer on side surfaces thereof.
 11. Thesemiconductor device of claim 8, wherein the first and second dielectriclayers comprise the same dielectric material.
 12. The semiconductordevice of claim 8, wherein the first and second dielectric layerscomprise different dielectric materials.
 13. The semiconductor device ofclaim 10, wherein each gate electrode structure further comprises: agate dielectric stack comprising a first oxide layer, a nitride layer onthe first oxide layer, and a second oxide layer on the nitride layer;and a gate electrode on the gate dielectric stack.
 14. The semiconductordevice of claim 12, wherein each dielectric layer comprises the samedielectric material.